As the global energy situation becomes more and more severe, it is an extremely urgent task to take full advantage of hydropower resources. In hydropower resource utilization projects, dam construction is an especially important link. Owing to a variety of factors in dam construction, such as long construction period, high investment, long ROI period, complex construction, significant impact on navigation and environment and so on, the utilization of hydropower resources develops very slowly. A great deal of hydropower resources can not be utilized fully and timely. Consequently, the energy crisis becomes more and more serious, and our living environment is increasingly deteriorated.
Presently, all dams are constructed with reinforced concrete. In view of the large size of dam, it is necessary to minimize the hydration heat and cost of concrete, namely, the amount of cement used should be minimized. Generally speaking, employing large-size aggregate can achieve that purpose. Therefore, usually the dam concrete is with degree 4 of gradation, in which the maximum size of aggregate can be up to 15 cm. However, if the conventional concrete adopts aggregate in larger size, it is suitable for use due to the limitation of mixing and vibrating capability.
Rock fill dam is a common dam type. At present, the common construction procedures of rolled rock fill dam are as follows: gather materials from the stock ground, transport the materials by truck directly onto the dam, and then roll the rock fill with a heavy vibrating roller to achieve the design compactness. Such construction procedures are simple and the dam construction cost is low. However, the size of rock fill dam is greater than the concrete dam; especially, rock fill dam usually has to be impervious, and therefore additional spillways must be arranged, which will result in significant increase of project cost. In addition, if clay core wall is used as the impervious body in rock fill dam, the construction will be easily interfered and will be sensitive to the climate, and the core wall may crack as a result of uneven subsidence. In recent years, reinforced concrete face rock fill dam has developed quickly, but there are still a lot of problems with regard to crack control of face.
There are mainly two existing concrete dam construction methods: column construction method and roller compacted concrete construction method.
The construction with typical column construction method is carried out by block placement, assisted with temperature control measures. That method has been widely applied in construction of concrete dams, such as the Three Gorges Concrete Gravity Dam in China. This method has obtained rich experience in assurance of concrete construction quality and concrete crack control, and presently the method is still the most commonly used method in concrete dam construction. However, with such a concrete construction method, a large quantity of formworks are required, and a variety of temperature control measures such as embedded cooling water pipes are required; in addition, the procedures are complex, the cost is high, and the construction speed is low.
The roller compacted concrete construction method was put forward by Professor Raphael (USA) in 1970s. This method employs zero-slump concrete and vibration rolling technique, characterized by high construction speed, simplified temperature control measures and low cost. More and more dams are constructed with roller compacted concrete nowadays, such as Shimenzi Arch Dam and Shapai Arch Dam in China. However, the inter-layer bonding strength of roller compacted concrete is relatively poor; especially, as a result of high construction speed and simplified temperature control, in the late stage of dam construction and early stage of dam operation, the concrete temperature is still high, therefore the built-up part may crack and has to be repaired. The cracks caused by temperature load are mainly a result of high hydration heat in roller compacted concrete, though the cement content in roller compacted concrete is lower than that in common concrete. To reduce the risk of cracking, structural measures such as induced joints and structural joints are taken for arch dams constructed with roller compacted concrete; however, the construction complexity is increased.